This invention relates to the programmable interconnection of digital circuits. Particularly, the invention relates to programmable interconnections known as crossbar switches, which are used to switch N digital inputs into N digital outputs.
Various interconnection schemes are possible, for example, as described in Wong et al. U.S. Pat. No. 4,871,930, blocks of programmable logic or logic array blocks (LABs) may be programmably interconnected using programmable interconnect arrays (PIAs). In this manner, relatively many small logic elements may be efficiently interconnected using a hierarchical method--first, interconnecting primitive logic elements into LABs, and second, interconnecting LABs using PIAs. The PIAs accept all logic function outputs from the LABs, and provide the means to programmably interconnect a small subset of these back into the LABs.
However, it is often desirable to provide digital circuit interconnections that programmably switch a number of inputs into an equal number of outputs. Further, it is desirable that the switching circuit have low standby power and display relatively small parasitic capacitance values. The switch should also be simple to program and low in cost.